Apparatus for controlling excess recharge current applied to a battery

Abstract

A battery recharge current source 12 provides a recharge current 14 to battery cells 16. Recharge current 14 is in excess of an optimum recharge current level for battery cells 16 and is divided into currents 26 and 28 by variable shunt load 24 as controlled by charge current control circuit 18. Charge current control circuit 18 is comprised of current sense circuit 20 and load control circuit 22. Current sense circuit 20 produces a current sense signal in response to current through battery cells 16. Load control circuit 22 is responsive to the current sense signal and controls variable shunt load 24 as needed to conduct excess current away from the battery cells.

What is claimed is: 
     
       1. A charge control circuit for controlling recharge current through a battery comprising: a control means responsive to recharge current through said battery; and   a variable shunt load responsive to said control means for conducting excess current away from said battery.   
     
     
       2. A charge control circuit as in claim 1, wherein said control means comprises: a current sense means for sensing current through said battery, and providing a current sense signal; and   a load control means responsive to said current sense signal for controlling said variable shunt load.   
     
     
       3. A charge control circuit as in claim 1, wherein said variable shunt load comprises a variable resistance element responsive to said control means. 
     
     
       4. A charge control circuit as in claim 2, wherein said current sense means comprises: a sense resistance coupled in series with said battery, thereby producing a voltage signal proportional to the recharge current through said battery; and   an amplifier means for amplifying said voltage signal by a preselected gain factor, and thereby producing said current sense signal.   
     
     
       5. A charge control circuit as in claim 2, wherein said load control means comprises: means for producing a reference voltage level; and   an amplifier means responsive to the difference of said current sense signal and said reference voltage level for producing a control signal for controlling said variable shunt load.   
     
     
       6. A charge control circuit as in claim 1, wherein said control circuit is resident in a battery pack. 
     
     
       7. A charge control circuit for controlling the recharge current through a battery, comprising: a current sense means responsive to said recharge current;   a variable shunt load electrically connected to said battery; and   a load control means responsive to said current sense means for controlling said variable shunt load to conduct excess recharge current away from said battery.   
     
     
       8. A charge control circuit as defined in claim 7, wherein said current sense means comprises: a sense resistor connected in series with said battery, thereby producing a voltage signal proportional to said recharge current through said battery; and   means for amplifying said voltage drop by a preselected gain factor.   
     
     
       9. A charge control circuit as defined in claim 7, wherein said variable shunt load comprises a pass transistor responsive to said load control means. 
     
     
       10. A charge control circuit as defined in claim 9, wherein said variable shunt load further comprises a resistor coupled in series with said pass transistor. 
     
     
       11. A battery pack having a charge control circuit for controlling recharge current through said battery pack, comprising: at least one battery cell;   a current sense means responsive to said recharge current, said current sense means comprising a sense resistor connected in series with said at least one battery cell, thereby producing a voltage signal proportional to current through said at least one battery cell, and means for amplifying said voltage drop by a preselected gain factor;   a variable shunt load electrically connected parallel to said at least one battery cell; and   a load control means responsive to said current sense means for controlling said variable shunt load to conduct excess recharge current away from said at least one battery cell.   
     
     
       12. A battery pack as defined in claim 11, wherein said variable shunt load comprises a pass transistor responsive to said load control means. 
     
     
       13. A battery pack as defined in claim 12, wherein said variable shunt load further comprises a fixed value resistor coupled in series with said pass transistor. 
     
     
       14. A battery pack as defined in claim 11 wherein said at least one battery cell is selected from the group consisting of lithium ion cells, lithium polymer cells, and sealed lead acid cells, and combinations thereof. 
     
     
       15. A rechargeable battery pack for use with a charger which provides a charge current level in excess of an optimum recharge current level, said battery pack having positive and negative terminals, said battery pack comprising: at least one battery cell;   a current sense circuit coupled in series with said at least one battery cell for sensing current through said at least one battery cell and producing a current sense signal;   a variable shunt load having a control input, and connected in parallel with said at least one battery cell and said current sense circuit; and   a load control circuit coupled between said current sense circuit and said variable shunt load, for producing a load control signal in response to said current sense signal.   
     
     
       16. A rechargeable battery pack as in claim 15, wherein said current sense circuit comprises: a sense resistor electrically coupled in series with said at least one battery cell, producing a voltage drop proportional to current through said at least one battery cell; and   an amplifier for amplifying said voltage drop by a preselected gain factor to produce said current sense signal, said current sense signal reaching a preselected threshold level when current through said at least one battery cell reaches said optimum recharge current level.   
     
     
       17. A rechargeable battery pack as in claim 15, wherein said variable shunt load comprises: a pass transistor having first and second conduction terminals and a bias terminal, said second conduction terminal connected to said negative terminal of said battery pack, said bias terminal being said control input of said variable shunt load; and   a fixed value resistor connected between said first conduction terminal of said pass transistor and said positive terminal of said battery pack.   
     
     
       18. A rechargeable battery pack as in claim 17 wherein said pass transistor is a MOSFET. 
     
     
       19. A rechargeable battery pack as in claim 17 wherein said pass transistor is a bipolar transistor. 
     
     
       20. A rechargeable battery pack as in claim 15, wherein said load control circuit comprises; a voltage reference for producing a reference voltage level; and   a comparator having an inverting input, a non-inverting input, and an output, said inverting input connected to said voltage reference, said non-inverting input connected to said current sense signal, said output resistively connected to said variable shunt load.